A process for charging an image carrier such as a photosensitive drum and a process for transferring a toner image on the image carrier to a recording paper or an intermediate transfer belt are absolutely required for an image forming apparatus based on the electrophotographic process. A charger and a transferor of a contact-type which are roller-shaped or brush-shaped can be employed for the processes. Due to contact with the image carrier and the intermediate transfer belt, the charger and the transferor suffer from friction damage. For that reason, recently, the charger, the transferor, etc. of a contact-type have been employed only for a relatively slow electrophotographic process. A high-speed electrophotographic process employs a corona charger (of a scorotron charger method etc.) Although the corona charger is suitable for the high-speed electrophotographic process, ozone generation is inevitable due to the structure thereof. Due to generation of ozone with a high concentration inside an image forming apparatus by the corona charger, products of ozone (such as NOx) adhere to the surface of the photoreceptor. This would cause a charge diffusion of the photoreceptor and result in an image defect, what is called an image blurring.
In order to prevent this, a general image forming apparatus is provided with an exhaust duct for forcibly exhausting ozone in the apparatus outside with an exhaust fan. Another type of an image forming apparatus is arranged such that a concentration of ozone to be exhausted outside the apparatus is reduced by further provision of an ozone decomposing filter inside the exhaust duct for exhausting ozone.
The ozone decomposing filter is applied not only to the image forming apparatus based on the electrophotographic process but also to an electrostatic air cleaning apparatus for dust, a waste ozone treatment device for an oxidation apparatus based on oxidizability of ozone, a preservation apparatus for fruits and vegetables utilizing an antiseptic effect of ozone, etc.
In addition to the ozone decomposing filter, Japanese Unexamined Patent Publication No. 42462/1990 (Tokukaihei 2-42462 (published on Feb. 13, 1990)) discloses a technique for heat decomposition of ozone with a heat source provided inside an exhaust duct for exhausting ozone.